The present invention relates to a charging apparatus for charging, for example, a battery pack.
There has been a charging apparatus for charging a secondary battery using DC voltage converted by a switching power supply from commercial power. A specific example of a secondary battery is a battery pack including batteries (called cells) connected in series and covered by an insulating outer case. For a lithium ion secondary battery, the battery pack is charged by a constant-current/constant-voltage (CC/CV) charging method, in which constant-current charging and constant-voltage charging are combined. An example of a charging apparatus of this type is described in Japanese Unexamined Patent Application Publication No. 2007-20299.
The charging apparatus described in Japanese Unexamined Patent Application Publication No. 2007-20299 has two error amplifiers (operational amplifiers): one for comparing the output voltage with a reference voltage and the other for comparing the voltage corresponding to a charging current with the reference voltage. The comparison outputs from the error amplifiers are supplied to a pulse width modulation control circuit, where output control is performed.